The present invention relates to a locking construction of an electrical connection box which contains electrical connection components such as a blade fuse, a slow blowing fuse, a relay, etc. and includes an upper casing member, e.g., an upper cover and a lower casing member such that the upper cover is mounted on the lower casing member for waterproofing.
FIG. 1 shows one example of a locking construction of a known electrical connection box. The known electrical connection box includes a lower casing member 1 made of resin and an upper casing member 2 or an upper cover. The upper casing member 2 is mounted on the lower casing member 1 so as to cover an upper opening of the lower casing member 1. In order to lock the lower and upper casing members 1 and 2 to each other, two upper locking portions 3, for example, are integrally formed on a front face 2a of the upper casing member 2 so as to downwardly extend like arms, while two lower locking portions 4 having an upwardly opening boxlike shape are formed at positions on a front face 1a of the lower casing member 1 corresponding to those of the upper locking portions 3, respectively.
As shown in FIG. 2, a forwardly extending boss 6 having a wedgy sectional shape is formed at a lower end of each of the upper locking portions 3. An upwardly oriented engageable face 10 is formed on an upper edge of the boss 6. Meanwhile, a rearward extending boss 7 having a wedgy sectional shape is formed on each of the lower locking portions 4. A downwardly oriented mating engageable face 11 is formed on a lower edge of the boss 7 so as to confront the engageable face 10. The upper locking portion 3 rides over the boss 7 of the lower locking portion 4 so as to be inserted into the lower locking portion 4 and the engageable face 10 and the mating engageable face 11 are brought into engagement with each other so as to lock the lower and upper casing members 1 and 2 to each other.
In the known locking construction of the electrical connection box, a proper clearance Co is formed between the engageable face 10 and the mating engageable face 11 as shown in FIG. 2. By setting the clearance Co at, for example, 0.2 to 0.8 mm, the lower and upper casing members 1 and 2 are locked to each other accurately and backlash is not produced at the time of locking of the lower and upper casing members 1 and 2. In order to clarify the clearance Co, the clearance Co is illustrated exaggeratedly in Fig. 2.
However, the upper and lower casing members 1 and 2 may be deformed at the time of their resin molding or distorted at the time of their mounting on a vehicle body. As a result, such a case happens that the clearance Co becomes smaller than the predetermined value referred to above. If the clearance Co becomes smaller than the predetermined value, such an inconvenience is incurred that the lower and upper casing members 1 and 2 are not locked to each other positively or it becomes difficult to lock the lower and upper casing members 1 and 2 to each other.